Cut-resistant yarns are used for making fabrics which resist abrasion, cutting, tearing, penetration and puncture. Such fabrics can be used to manufacture protective garments for workers in various industries working with abrasive materials or sharp objects, as well as for police and military personnel requiring protection against stabbing implements and projectiles.
Cut-resistant yarns can be made from glass, mineral fibres, steel, but increasingly, synthetic polymer fibres are being employed, because they provide excellent cut-resistance, while offering a weight advantage, and a look and feel in the finished fabric that is similar if not identical to regular fabric. Polymers that are used for cut-resistant yarns include, for example, polyamides (e.g., p- and m-aramids), polyolefins (e.g., polyethylene), and polyazoles (e.g., PBO), and PIPD (poly-diimidazol pyridinylene dihydroxy phenylene, “PB”).
Yarns made from synthetic polymer fibres are made using various spinning processes, all of which involve the use of a spinneret having multiple small openings, through which a concentrated solution or suspension of the polymer (or molten polymer) is sprayed or extruded. After extrusion, the polymer solidifies (and consolidates) into filaments, which are then spun into a multifilament yarn.
Examples of such spinning processes are described in the prior art. U.S. Pat. No. 4,078,034 discloses a method called “air gap spinning” in which a solution of an aromatic polyamide is extruded from a spinneret into an air gap (approximately 9 mm) before passing into a coagulating bath. In the case of poly(p-phenylene terephthalamide) (p-aramid), the solution consists of 15-25% by weight p-aramid in concentrated H2SO4, and the coagulating solution contains <20 wt % aqueous H2SO4, at a temperature which is adjusted to below 35° C. for this quenching step.
In a process used for spinning m-aramid, a concentrated solution of m-aramid in an amide solvent, such as N,N-dimethylacetamide (DMA) is extruded from a spinneret into an aqueous coagulation bath. Such a process is disclosed in U.S. Pat. No. 4,073,837.
The holes in the spinneret head are chosen to produce filaments of the desired number and diameter. Filaments can be extended in air or gas before solidification (often referred to as “spin-stretch”), and/or in a liquid during the quenching/solidification process, and in many products by drawing after the filaments have been initially quenched or solidified. Drawing the filaments will reduce the average diameter. Multiple filaments are spun together to produce a yarn having a final linear density that is a sum of the linear density of each of the filaments.
Although existing synthetic yarns made with conventional spinning processes have excellent cut- and most of the time moderate abrasion-resistance, a need remains for yarns with excellent cut- and improved abrasion-resistance.